This research project is concerned with infants' perception and knowledge of bimodally-specified objects. Specifically, it deals with an infant's ability to determine the source of a sound and its movement by detecting invariant relationships given in optic and acoustic stimulation. Two experiments are proposed. In one infants' visual tracking of a sound-making object will be monitored to determine whether sounds coresponding to the object's motion (continuous or discontinuous) will enhance tracking. The second experiment asks whether infants perceive and relationship between the increasing or decreasing volume of a sound and the approach or withdrawal of an object. In each case the underlying question is whether infants perceive bimodally-specified, unitary objects when information is invariant over the auditory and visual sense modalities. As such, the project is concerned with the development of behavior as determined by psychological factors--in particular how the developing infant abstracts and uses information from the environment to understand his/her physical environment.